1. Field of the Invention
This invention relates to an electrical cable suitable for distributing an alternating current and signals and more specifically relates to an electrical cable having a plurality of conductors in which at least some of the conductors transmit electrical signals subject to cross talk. In particular, this invention relates to a cable suitable for use in distributing electrical power, data signals suitable for use in control applications and electrical signals suitable for use in telephonic communications.
2. Description of the Prior Art
Standard building and electrical codes require the separation of cables used in the distribution of electrical power and for transmission of signals, such as telephone signals or data signals. Recently, more sophisticated systems have been proposed in which the integrated distribution of power, and signals within a building would provide some significant advances in the wiring in the building. For example, it has been proposed that power, data, control and entertainment cabling be integrated into a single cable, both to provide ease of installation and to advance the capabilities of the wiring. One suggested approach is the use of a closed loop power system in which electrical power is delivered to an outlet receptacle or to a component attached to the wiring system only in response to receipt of certain signal intelligence indicating both the need for the presence of a current and indicating that current can be safely transmitted without shorts or opens. Such a system would require an intelligent controller which must be interconnected by data lines. In order to insure that the additional wiring necessary for such a closed loop system could be easily installed within a structure, it has been suggested that power lines, telephone communication lines, integrated cabling and the control lines used for such a system be incorporated into a single cable. To provide for ease of termination, it has been suggested that such a cable would be generally flat and would include three power conductors, a hot, a neutral and a ground, for carrying 60 Hertz 20 amp and 15 amp RMS current. Five data conductors, consisting of two data lines, two clock lines and data ground, would be employed in the same cable. Four telephone lines suitable for either digital or analog transmission would also be included. In order to insure that the control logic in such a system would be continuously supplied with power, two 12 volt DC lines could also be included in such cable. By using a flat ribbon cable configuration, it would be possible to employ an insulation displacement connector to terminate all of these conductors in one operation. In addition to these conductors, such a cable could also include one or two coaxial cables to provide communications or RF entertainment signals which could not be established using the unshielded conductors in the remainder of the cable.
Installation of these relatively wide ribbon cables in a conventional building structure by a conventional construction technique however, introduces certain complications. For instance, unless the cable is bundled into a circular or oval configuration, it would be necessary to drill oblong holes in the studs of a frame structure to route the conductors in a building, such as a home. However, if the cables are bundled, crosstalk can be introduced between the telephone and the data conductors or between the 60 Hertz power conductors and either the telephone or data lines. Compensation for this crosstalk could be provided by incorporating shielding between varying lines, both signal and power, of such a cable. However, if shielding is provided to permit the bundling or grouping of conductors in a circular or oval arrangement, the cost, rigidity and complexity of the cable is increased. The instant invention provides a means for bundling a cable having each of these different transmission media incorporated into a single flat ribbon cable while at the same time preventing excessive crosstalk in the various signal lines.
Multi-media bundled cable which have been previously proposed, either have not taken the crosstalk into account, or have solved that problem by providing shielding around the plurality of the conductors. For example, U.S. Pat. No. 4,533,790 discloses a cable including power supply, telephone and communications or data conductors. The communication or data conductors comprise coaxial conductors and the power supply conductors are surrounded by a shield. In that cable the separate conductors are grouped into separate circular bundles which are interconnected by webs. In any cable in which discrete conductors are positioned in a circular bundle, termination of the conductors requires separation and orientation of specific conductors. Significant benefits of simple mass termination using insulation displacement contacts are lost for a cable of this configuration.
U.S. Pat. No. 4,149,026 and U.S. Pat. No. 4,217,155 disclose a multi-pair cable having low crosstalk in which the respective conductors are so spaced as to effectively form a balanced compacitive bridge configuration. Thus, a low profile, low crosstalk cable suitable for use in undercarpet wiring applications is provided. Those patents however, do not envision the use of a bundled configuration formed initially from a flat cable containing multiple media connectors, such as data, telephone and power conductors.
U.S. Pat. No. 4,758,536 discloses a cable and connector system for use with flat cable containing a plurality of signal conductors and hot, neutral and ground power supply conductors, all located in the same web. Although this patent clearly shows the advantages to be gained from the use of mass termination insulation displacement contacts with a flat cable with conductors spaced side by side, crosstalk problems in a round bundled cable are not accounted for in this patent.